Our European Patent Application No. 78300203.3 (Publication No. 0001473; the disclosure of this Application is incorporated herein by reference) discloses inter alia compounds of general formula (I): ##STR1## wherein each of Z and Y, which may be the same or different, is hydrogen, fluorine, chlorine, bromine, iodine, trifluoromethyl, difluoromethyl or chlorodifluoromethyl, provided at least one of Z and Y is trifluoromethyl, difluoromethyl or chlorodifluoromethyl; and R.sup.1 is cyano; carboxy; a group of general formula --CONR.sup.2 R.sup.3 wherein R.sup.2 is hydrogen or alkyl and R.sup.3 is hydrogen, C.sub.1-4 alkoxy, optionally hydroxy- or phenyl-substituted C.sub.1-4 alkyl, optionally halo-substituted phenyl, a group of general formula --NR.sup.4 R.sup.5 wherein R.sup.4 is hydrogen or C.sub.1-4 alkyl and R.sup.5 is hydrogen, C.sub.1-4 alkyl or optionally halo-substituted phenyl, or R.sup.2 and R.sup.3 form together with the nitrogen to which they are attached pyrrolidino, piperidino or morpholino; a group of general formula --COSR.sup.6 wherein R.sup.6 is alkyl or phenyl; optionally halo-, alkoxy- or hydroxy-substituted alkoxycarbonyl; a group of general formula: ##STR2## wherein Z and Y are as defined above and Q is alkylene; a group of general formula --CO(OCH.sub.2 CH.sub.2).sub.n OR.sup.7 wherein R.sup.7 is C.sub.1-4 alkyl and n is an integer of 1 to 5; optionally halo- or methyl-substituted cyclohexyloxycarbonyl; (C.sub.3-6 alkenyl) oxycarbonyl; optionally halo- or methyl-substituted phenoxycarbonyl; or benzyloxycarbonyl, the phenyl moiety of which being optionally ring-substituted with halogen or methyl; and, in the case of compounds wherein R.sup.1 is carboxyl, the salts of said compounds. The compounds have selective herbicidal activity.
The above compounds can be prepared, and this forms part of the present invention, by reducing a compound of general formula (II): ##STR3## wherein Z, Y and R.sup.1 are as defined above, and if necessary, when R.sup.1 in the compound of general formula (I) so obtained is not the desired group, converting it in known manner to give a compound of general formula (I) where R.sup.1 is the desired group.
The compounds of general formula (II) can be prepared (a) by reacting a compound of general formula (III): ##STR4## wherein R.sup.1 is as defined above, or a salt (for example an alkali metal, e.g. sodium or potassium salt) thereof, with a compound of general formula (IV): ##STR5## wherein Z and Y are as defined above and X is halogen (e.g. fluorine, chlorine or bromine); or (b) by reacting a compound of general formula (V): ##STR6## where Z and Y are as defined above, or a salt thereof, with a compound of general formula (VI): ##STR7## wherein R.sup.1 and X are as defined above; and, when R.sup.1 in the compound of general formula (II) obtained in (a) or (b) is not the desired group, converting it in known manner to give a compound of general formula (II) where R.sup.1 is the desired group.
The compounds of general formula (III) can be prepared by reacting hydroquinone or a salt thereof (for example a di-alkali metal salt e.g. a di-sodium or potassium salt) with a compound of general formula (VI) wherein R.sup.1 and X are as defined above, and when R.sup.1 in the compound of general formula (III) so obtained is not the desired group, converting it in known manner to give a compound of general formula (III) where R.sup.1 is the desired group.
The process can be illustrated by the reaction sequences given below for the preparation of the compound of general formula (I) wherein Z is trifluoromethyl, Y is hydrogen and R.sup.1 is n-butyl: ##STR8##
The preparation of the compound of general formula (II) by reacting the compound of general formula (V) and the compound of general formula (VI) and the preparation of the compound of general formula (III) by reacting hydroquinone or a salt thereof with a compound of general formula (VI) can be performed by reacting (e.g. by heating) the ingredients in a polar solvent (for example acetone) in the presence of a dry base for example an alkali metal carbonate (e.g. sodium or potassium carbonate). Preferably, in the latter reaction, only one equivalent of the compound of general formula (VI) is used and preferably again the compound of general formula (VI) is added to a preformed mixture of hydroquinone and the base. Suitably the compound of general formula VI is used or stored in association with a polymerisation inhibitor. After the reaction, the reaction mixture can be poured into water, and the mixture so obtained concentrated and extracted with a suitable solvent. After evaporation of the solvent, the residue so obtained can be purified by distillation.
The reaction of the compound of general formula (III) with the compound of general formula (IV) to give the compound of general formula (II) is suitably performed in the presence of a dry base and a solvent or diluent. Examples of suitable solvents are lower alkyl ketones, for example methyl ethyl ketone. The reaction may be accelerated by heating and may for example be conveniently carried out at the reflux temperature of the solvent. Examples of suitable bases are inorganic bases such as sodium or potassium carbonate. If desired, a mixture of a compound of general formula (IV) wherein X is chlorine with a compound wherein X is fluorine can be used.
Suitable ways of carrying out the reduction step can be found for example in Harrison and Harrison, Compendium of Organic Synthetic Methods, 1971, Volume I, pages 198 to 202, published by Wiley Interscience), the disclosure of which document is incorporated herein by reference. One way is to hydrogenate the compound of general formula (II) in the presence of a palladium or platinum catalyst and a suitable solvent. After the hydrogenation, the catalyst can be filtered off and the solvent removed to give the product as an oil which can be purified by chromatography, distillation or crystallisation.
As indicated above, the group R.sup.1 in the compounds of general formula (I), (II) and (III) can be converted to another group R.sup.1. For example, the compounds wherein R.sup.1 is an ester group can be hydrolysed to the corresponding acid and then the amides, salts and other esters can be prepared from the acid by methods known in the art. Alternatively, transesterification techniques can be used to prepare other esters.
The compounds of general formula (II) and (III) are novel compounds, and as such form part of the present invention.
Hydroquinone and the compounds of general formula (IV) and (VI) are old compounds; they can be prepared by methods known in the art. The compounds of general formula (V) and details of their preparation are disclosed in European Patent Application No. 78300203.3.
The compounds of general formula (I) contain a chiral centre. One of the enantiomers is believed to be a more active herbicide than the other enantiomer. For example, in the case of the compounds of general formula (I) wherein Z is trifluoromethyl and Y is hydrogen, the D(+)enantiomer is more active than the corresponding L(-)enantiomer. Our European Patent Application No. 79300234.6 (Publication No. 0003890; the disclosure of this Application is incorporated herein by reference) discloses more details of the enantiomers. Such enantiomers can be obtained in the substantially pure state by resolution of the racemic mixture of the compound of general formula (I) or alternatively the reduction stage can be performed in the presence of a suitable chiral catalyst in order to produce the desired enantiomer direct. Suitable chiral catalysts are for example the Wilkinson's catalysts rhodium [1,2-bis(O-anisylphenylphosphino)ethane] or a rhodium-chiral-O-anisylcyclohexylmethylphosphine complex.
The compounds of general formula (II) have herbicidal activity; they are in general more effective against grass species than against broad-leafed species of plants.